If you don't like the way your keyboard is laid out, a keyboard remapper can change it. There are only a few for Mac OS X, and the lack of development on many of your options makes your choice pretty easy. Regardless, KeyRemap4Macbook would rise to the top thanks to numerous remapping options, customizability, and helpful bonus features.

Additional apps (PCKeyboardHack and NoEjectDelay) are available for additional functionality.

Includes a built-in uninstaller.

Supports Growl notifications.

KeyboardRemap4MacBook is a powerful keyboard remapper that can change not only the functionality of keys and key combinations, but just about everything related to how a key repeats when you hold it down. Keyboard remappings are highly customizable (although it's not a simple process—see below). You can change practically anything, and many choices are already available for you. You can search through all the options and quickly find what you're looking for, or just browse by category. KeyboardRemap4MacBook can even completely remap your keyboard for different languages or even the Dvorak layout. It's very powerful and usage is pretty straightforward (with one exception, mentioned below).

The downside is that keyboard remapping functions are predefined and you can just check them off. If you want to add custom remapping functions, you have to edit an XML file. When you're using a GUI application this is not exactly the ideal experience. That said, this is the only significant drawback.

Although there's no full built-in keyboard remapper for Mac OS X, you can remap shortcuts. You can also remap modifier keys in the Keyboard System Preferences pane. While this feature is slim competition for a true keyboard remapper, often times this is all some users want to do. If you're primarily interested in changing shortcuts and don't care much for other functionality, you don't really need to install anything at all.

DoubleCommand (Free) was a popular keyboard remapper, but it hasn't been updated since November of 2009. Currently the developer of DoubleCommand recommends checking out KeyboardRemap4Macbook instead if it can't handle certain features of your newer keyboard. KeyboardRemap4Macbook, overall, is a more capable application.

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